In underwire brassieres it is the common practice to provide a tubular pocket or sheath below a brassiere cup in which a "wire", frequently referred to as an "underwire" is received to assist in maintaining the shape of the cup.
In early versions of the underwire brassiere, the wire itself was of circular cross section and composed of metal with a high degree of stiffness, thereby imparting significant rigidity to the brassiere. Because that wire tended to pierce through the fabric of the brassiere, it could pose a danger to the wearer and complicated the laundering of the brassiere. Insertion of the wire into the tubular sheath of the cup also posed a problem because of the high rigidity of the wire.
As a consequence, plastic wires were developed as brassiere underwires with the advantage that the flexibility of the underwire was improved. These underwires could have a flattened cross section to enhance stiffness in the wire plane while affording some flexibility transversely thereto. It has also been proposed to stitch the plastic wire in place through at least one end of the wires, usually the end of the underwire located at the cleft in the brassiere between the two cups, while the opposite end of the wire, toward the outside of the brassiere tended to move free in the tubular sheath or pocket. Even with such plastic underwires, there was considerable stiffness which could lead to discomforture of the wearer.
There have been proposals for underwires which are not preformed and which are so flexible that they assume the shape of the sheath or pocket without contributing any preform to the shape. These wires have the advantage that the brassiere cup can have considerable flexibility and thus can be more comfortable and can be washed without any danger that the wire will pierce through the fabric and snag on other garments during the laundering process. However, such totally flexible wires do not significantly contribute to shaping of the cup and do not satisfy the need for imparting a certain shape to the brassiere cup both in use and when the brassiere is on a hanger to satisfy the wearer.
Mention may also be made of the fact that heretofore, with relatively stiff underwires, the brassiere designers were compelled to have the underwire fabricated to precisely fit the sheath or tube formed in the brassiere so as to avoid damage to the fabric by the wire with time. The need to have specially designed wires to fit any particular brassiere design greatly complicated brassiere manufacture. Of course, when totally flexible wires were used, this problem did not arise, but the brassiere designer was compelled to accept the fact that the underwire could not contribute adequately to the desired configuration of the brassiere.
Finally, it may be noted that the preformed underwires heretofore marketed and used commercially and successfully have had the configuration of a "U" or an arc segment with one or more centers of curvature and ends which extend parallel to one another or diverge with respect to one another so as to constitute generally open arcs. This configuration was vital for stiff wires so as to prevent pinching of the breast when received in the cup and to allow mobility of the brassiere on fitting and outer wearing.